1. Field of the Invention
The present invention relates to a high-frequency sputtering device for manufacturing a magnetic reproducing head of a magnetic disc driver, a storage element of a magnetic random access memory and a magnetic sensor, and a manufacturing method thereof.
2. Related Background Art
Since a tunnel magnetoresistive thin film using insulating film MgO as a tunnel barrier layer exhibits extremely high rate of magnetoresistance change of 200% or more at room temperature, application to a magnetic reproducing head and a storage element of MRAM is expected. In order to achieve high resolution of a magnetic head and high integration of MRAMs, there is demand for the size reduction of their elements, however, in order to ensure high speed transfer of data, it is indispensable to reduce junction resistance. Although, it is possible to reduce junction resistance by reducing the thickness of the tunnel barrier layer of MgO film, there has been a problem that the rate of magnetoresistance change is also reduced at the same time. The reason may be that crystalline orientation at an initial stage of growth of the MgO film has been disturbed.
Since plasma density in case of high-frequency sputtering is higher than that in case of DC sputtering, and a bias voltage in case of high-frequency sputtering is more easily applied to a structure contacting with plasma than in case of DC sputtering, positive ions accelerated by potential difference between the substrate and the plasma flow into a substrate more easily in case of high-frequency sputtering than in case of DC sputtering, Since the inflow of positive ions having this energy to the substrate promotes surface diffusion of sputtering atoms on the substrate, a high density and highly oriented film can be formed. However, if a bias potential on the substrate is too high, a problem that high energy positive ions damage a film during formation, will occur. That is, there is an optimum range of the substrate potential in order to form a high-quality thin film, thereby, it is important to control the range. Here, it is also necessary to consider that as an insulating film is deposited on a substrate the substrate potential changes gradually.
In Patent Document 1, a technology in which the potential of a substrate electrode with respect to an anode electrode can be changed by changing the value of variable resistance disposed to the substrate electrode in a high-frequency sputtering device, is disclosed. In Patent Document 2, a high-frequency sputtering device in which an electrode for controlling particles incident to a substrate is disposed between the substrate and a target, is disclosed.
Patent Document 1: Japanese Patent Laid Open No. 09-302464
Patent Document 2: Japanese Patent Laid Open No. 06-179968